Lead-free solder has been much more required recently due to problems such as waste disposal of electronic devices and for protecting the environment.
On the other hand, Pb--Sn based solder is generally used for soldering electronic parts. Pb--Sn based solder has good connectability, and thus the melting point can be selected in a wide range by controlling the ratio. In such solders, 63 wt % Sn--Pb eutectic solder generally has been used since it enables soldering of electronic parts at a lower temperature with less thermal influence on the electronic parts since its melting point is only 183.degree. C.
During a process for installing electronic parts, the soldered portion may be heated once again in an installed electronic part. For example, in a process for manufacturing a semiconductor device, the die is heated after the semiconductor element chip is soldered to a lead frame (e.g. a die) for wire-bonding. In a hybrid IC where electronic parts are installed on both surfaces of a printed circuit board, one side is provided with electronic parts and soldered after the other side is treated likewise. The electronic elements will be heated also by their own heat even after the installation.
In order to avoid the above-mentioned problems, the first soldering materials are required to have a higher liquidus temperature, so that the first-bonded parts will not fall out during a second heating. Such a high temperature soldering material should have a liquidus temperature ranging from 200 to 350.degree. C.
Unexamined Published Japanese Patent Application No. 61-156823 discloses a lead-free high-temperature solder material whose liquidus temperature ranges from 200 to 350.degree. C. The Sn--Cu based material mainly comprises Sn to which small amount of Cu is added. Unexamined Published Japanese Patent Application No. 61-55774 discloses Sn--In based lead-free solder material and No. 62-163335 discloses Sn--Cu--Zn based material.
Unexamined Published Japanese Patent Application No. 6-685 discloses that metallic or insulator particles are added to a material to be die-bonded by pressure-adhering in order to control the thickness of the die bond material.
However, if the conventional lead-free high temperature solder materials such as Sn--Cu are used for die-bonding or soldering of heating parts such as a hybrid IC, the high temperature solder is cracked and the conduction is worsened after the electronic device is used for a long time. This is caused by thermal fatigue due to the heat cycle. Heat cycle means repeated temperature change, for example the inside of an electronic device being heated by its electronic parts when used, and the temperature returning to room temperature after that. As previously known, the conventional lead-free high temperature solder material is inferior in the thermal fatigue properties. Therefore, lead-containing high temperature solder has been widely used in order to improve thermal fatigue property. Some other conventional lead-free high temperature soldering materials are not good in soldering properties.